1. Field of the Invention
The present invention relates to: a transmission managing apparatus which, in an information transmitting system for using serial buses to connect a plurality of information processing apparatuses to each other and transmitting information mutually between the information processing apparatuses, manages the condition in the transmission of the information; the information processing apparatus included in the information transmitting system together with the transmission managing apparatus; and the information transmitting system including the transmission managing apparatus and the information processing apparatus.
2. Description of the Related Art
Recently, a so-called IEEE 1394 standard (a regular name is “IEEE (Institute of Electrical and Electronic Engineers) Std. 1394-1995 IEEE Standard for a High Performance serial Bus”) is published as a new standard to transmit information in real time through serial bus Between a plurality of information processing apparatuses (for example, between a personal computer and a digital video camera or MD (Mini Disc) and the like). Accordingly, a digital video camera, a personal computer and the like having serial ports in accordance with the IEEE 1394 standard have been manufactured.
This IEEE 1394 standard standardizes that a plurality of information processors (hereafter, merely referred to as nodes) are connected to each other through serial buses to then transmit in time division the information corresponding to a plurality of channels between the respective channels (this standard standardizes that information can be transmitted by using a maximum of 63 different channels within a system connected through one serial bus).
Here, the IEEE 1394 standard standardizes the execution of an initialization of a serial bus referred to as a so-called “bus reset”, when another node is newly connected to node groups already connected to each other through the serial buses (namely, at a time of bus connection), or when one node is disconnected from the node groups (namely, at a time of bus open). Then, the following processes are executed in conjunction with the bus reset to accordingly establish a new connection condition (hereafter, the connection condition is referred to as a “topology”).
(1) In conjunction with an occurrence of a bus reset, a bus reset signal indicative of the occurrence of the bus reset is transmitted to all nodes in which a node detecting the occurrence of the bus reset (namely, a node to which another node is newly connected, or a node from which an existing connection is disconnected) is connected to a serial bus.(2) Next, a tree identification to connect the respective nodes onto a tree is carried out after the bus reset. Then, a node located at a vertex of the connected tree is recognized as a route node.(3) Next, the recognized route node makes each node recognize an identification number (ID number) peculiar to each node to identify each node within a tree system.(4) Next, an IRM (Isochronous Resource Manager) node is set which is a node for managing the communication states (actually, channels used by the respective nodes and later-described transmission occupation periods) in all the nodes in the generated tree, and then displaying the current usage channels and the transmission occupation periods currently occupied by the respective nodes, in such a condition that can be identified by the other nodes.(5) Finally, a bus manger is set which is a node for controlling the information transmission states of all the nodes.
A new topology after the bus reset is established through the above-mentioned process composed of five steps.
Then, in case that the information is actually transmitted after the establishment of the topology, a transmission node which is a node trying to start transmitting the information inquires of the IRM nodes the current communication states of the other nodes. If it is possible to use a channel and a transmission occupation period that the transmission node desires to use, the transmission node obtains a right of transmitting the information (actually, the transmission node insures the channel and the later-described transmission occupation period which the transmission node desires to use), and then starts the transmission of the information. At this time, immediately before the transmission of the information, the transmission node transmits to the IRM nodes a report of re-writing a display of a communication state in the IRM node (namely, since the start of the transmission of the information in the transmission node causes the transmission occupation period and the channel currently being used on the serial bus to be changed, it is necessary to re-write the displayed content into a new communication state after this change). The IRM nodes receiving this report respectively execute a process of updating the displayed content. After that, the content displayed after the update can be referred by the other nodes.
The transmission occupation period will be schematically described below.
In the IEEE 1394 standard, the information from each node is transmitted as collection for each information unit referred to as an “isochronous cycle” (here, this “cycle” implies one cycle generated after division in time sharing on a serial bus). This isochronous cycle includes an isochronous transmission portion containing the information transmitted synchronously with the information included in another isochronous cycle (e.g., video information or audio information) and an asynchronous transmission portion containing the information transmitted asynchronously with and independently of other information (e.g., control information to control an output of the video information or the audio information). Then, the information within this isochronous transmission portion is divided in time sharing for each different channel, and different information is transmitted for each channel.
At this time, in the isochronous transmission area, it is standardized that a temporal length of the isochronous transmission area within one isochronous cycle is 100 μa sec at its maximum. Thus, it is necessary that a total period occupied by the information assigned to each channel within one isochronous transmission area for its transmission is also 100 μsec or less. At this time, a transmission period within the isochronous cycle occupied by the one channel is the above-mentioned “transmission occupation period”.
In addition, this transmission occupation period may be referred to as a “usage band” of a serial bus depending on a case, or it may be referred to as a “usage capacity” of a serial bus. On the other hand, if a length of the isochronous transmission area is less than 100 μsec within the one isochronous cycle (including a case of zero), a period within an isochronous cycle other than the isochronous transmission area is used only as the asynchronous transmission area.
However, according to the IEEE 1394 standard having the above-mentioned configuration, when each transmission node starts transmitting the information, each transmission node needs to start the transmission after inquiring of the IRM node a communication state on the serial bus, checking whether or not a channel and a transmission occupation period which each transmission node desires to use can be actually used, and then insuring them if they can be used (in addition, those inquiring, checking and insuring operations are typically referred to as an “arbitration operation” on the standard).
This necessity implies the following necessity, in other words. That is, if the channel and the transmission occupation period which the transmission node desires to use cannot be used, the transmission node transiently holds the start of the information transmission. After that, it again inquires of the IRM node the channel and the transmission occupation period, and starts the information transmission only after checking and confirming that the desired channel and transmission occupation period can be used.
At this time, if the channel and the transmission occupation period cannot be insured when the inquiry as to the IRM node is once carried out, the similarly referring and insuring operations are again repeated after a wait of a preset predetermined period. However, in this case, if the communication state on the serial bus is not updated in the predetermined period (the communication state on the serial bus (i.e., the channel currently being used and the transmission occupation period currently being occupied) is not always changed in the predetermined period), this results in a problem that the transmission node needs to repeat a useless and meaningless operation of insuring the channel and the transmission occupation period which can not be insured.
In view of the whole serial buses, this problem leads to a problem that it is necessary to transmit a control signal necessary for the useless insuring operation and the like by dividing a part of the asynchronous transmission area having an upper limit, and there may be a case in which other necessary control signals and the like can not be transmitted at this time.
On the other hand, from the viewpoints of the situations of the respective nodes, the above-mentioned problems lead to a problem that the repetition of the useless insuring operation increases the burdens on the signal processes in the respective nodes.